The first step is to run Malwarebytes Free ( www.malwarebytes.org ) to make sure you haven't picked up any malware. Unlikely in this case but its best to be sure.

Then try these steps:

1. Perform a clean boot (http://support.microsoft.com/kb/929135) Since the problem is intermitant, you may have to do several Clean Boots after running your typical programs.
2. Disable fast Boot - http://winaero.com/blog/how-to-disab...n-windows-8-1/
3. Disable Dynamic processor fast ticks:
Open an elevated command prompt and type the following command:
bcdedit /set disabledynamictick yes
If it doesn't help, re enable fast ticks:
Use the following command (also type it in an elevated command prompt):
bcdedit /set disabledynamictick no